The date is conjectured on the assumption that the person mentioned in the letter is Karl Gustav Wilhelm Stenzel, who wrote on leaf position and movement in conifers. CD was carrying out research for Movement in plants, which was published in November 1880, during this time. See also n. 2, below. Williams & Norgate were CD’s usual booksellers.

It is unlikely that CD referred to Edmund Max Stengel, the philologist; it is possible that ‘Stengel’ is a mistranscription of ‘Stenzel’. Karl Gustav Wilhelm Stenzel is not mentioned elsewhere in CD’s correspondence or in CD’s publications. There is a lightly scored note by Stenzel, ‘Zweige einer Edeltanne’ (Branches of a silver fir; Bericht über die Thätigkeit der botanischen Section der Schlesischen Gesellschaft, 15 January 1880, pp. 135–6), in the Darwin Pamphlet Collection–CUL. Stenzel’s note related to the position of leaves of new shoots, a topic that interested CD and Francis Darwin when they worked on Movement in plants. The cover of the pamphlet containing the note is marked ‘Dr Francis Darwin’.